It is known from German open application 31 40 582 that the cooling air, brought up from the bottom to the cooling area of a shaft furnace for cooling the burned and sintered goods and which gets heated in this cooling process, can be aspirated in the upper part of the cooling area and supplied to the burner as combustion air. In the case of such a shaft furnace the heat consumption is noticeably lower, since the heat content of the cooling air is used for the combustion process.
Unfortunately the quality of the aspirated reheated cooling air is variable in its heat and oxygen content. This has proven to be a disadvantage since it leads to undesired oscillations of the temperature in the combustion area.
The object of this invention is to make possible the use of the heat content of the reheated aspirated cooling air to supply the burner with combustion air having a constant heat and oxygen level.